using System;

public class Program

{

    public class TimeSpanFormatProvider: IFormatProvider, ICustomFormatter

    {

        public object GetFormat(Type formatType)

        {

            return this;

        }

        public string Format(string? format, object? arg, IFormatProvider? formatProvider)

        {

            return "test";  

        }

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        TimeSpan t = TimeSpan.FromMilliseconds(100101012);

        string str = t.ToString("ms", new TimeSpanFormatProvider());

        Console.WriteLine(str);     

        str = string.Format(new TimeSpanFormatProvider(), "{0:ms}", t);

        Console.WriteLine(str);

    }

}